Double End Submerged Arc Welding (DSAW)
Submerged Arc Welding (SAW) pipe is named for the welding process in which the arc is submerged in flux. When heated to welding temperature, the flux protects the steel in the weld area from any impurities in the air. When internal and external welds are made simultaneously, the welding is accomplished in a separate process and the pipe is considered Double Side Submerged Arc Welded (DSAW).
Pipes produced by the DSAW process fall into three common types.
--- U&O Method
The U&O method is so named because it uses a "U" press followed by an "O" press to form the cylinder from 40-foot long plates ordered by size and grade. The cylinder is then welded inside and out using a submerged arc process with up to five wires. Most U&Os use mechanical or hydraulic cold expansion. When cold expanded, the yield strength of LSAW pipe increases. This method of pipe production produces superior quality and precise dimensional tolerances. The primary use of this type of pipe is for natural gas and oil transportation. It requires a large minimum tonnage for sizing and is only produced domestically in 40-foot lengths.
---Rolling and Welding
This manufacturing method is also known as the "pyramid roll method" because it uses three rolls arranged in a pyramid structure. Plates, sorted by grade and thickness, are rolled back and forth between the pyramid-shaped rolls until a cylinder is formed. The cylinders are then moved to a welding station. Most pyramid rolls are 20 feet or less in length.
Larger lengths can be achieved by ring welding 5-, 10-, or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without intermediate welds, and the only producer capable of sizing the product.
The advantages of rolled and welded pipe are small rolled quantities and short lead times. It is possible to produce very large diameters (ID or OD) and extremely thick walls. Due to the short length of the tank, it is easy to realize the production of composite piles or pieces with different yields and tensile strengths. This material is slow to produce and is costly due to multiple girth welds.
---Spiral Weld
Spiral welded pipe is a type of steel pipe that has a helical DSAW weld throughout the length of the pipe. The outside diameter is determined by the angle between the uncoiled steel and the forming head. The sharper the angle, the larger the diameter. The production of large hot rolled coils of sufficient width and the development of reliable non-destructive testing methods have enabled the product to be used in more demanding applications.
Spiral-welded pipe can be precision coiled in lengths up to 115 feet, with inside or outside diameter sizes up to
144 inches. Minimum tonnage is required for rolling. Because of the slow manufacturing process, this provides contractors with the advantage of short-term order changes. The same slow production can be a disadvantage when large tonnages are required and lead times are short. Spiral welded pipe is produced in limited sizes.
